The invention relates to a device for detecting the reverse rotation of a rotating part of an internal combustion engine as generically defined by the preamble to the main claim.
In multi-cylinder internal combustion engines with electronically regulated injection and ignition, a calculation is executed in the control unit as to when and how much fuel is to be injected into which cylinder and when ignition should occur. In order for these calculations to be executed correctly, the respective positions of the crankshaft and camshaft of the engine must be known.
EP 0 017 933, for example, describes the fact that the crankshaft and camshaft are each connected to a disk whose surface has at least one reference mark on it in the form of a gap and also has a multitude of similar markings, also called increments, on it. These two rotating disks are scanned by suitable stationary sensors. Based on the chronological sequence of impulses supplied by the sensors, the control unit can obtain definite evidence as to the position of the crankshaft and camshaft so that corresponding control signals for the injection or ignition can be produced in the control unit. In order to assure that the position of the crankshaft and the camshaft is correct, a synchronization must be executed after the engine is started. This is carried out based on the detection of the reference marks. The speed and angular position of the crankshaft and camshaft must be determined in a highly precise manner.
Based on the fact that in one work cycle of a four-stroke engine, the camshaft executes a 360xc2x0 KW, the crankshaft executes a 720xc2x0 KW during the same interval, and the positions of both shafts can be detected by means of reference marks, a determination can be made as to which work cycle the engine is currently in. In order to determine the speed of a crankshaft, a detector disk with 60-2 teeth is usually used, which is scanned by a sensor inductively, magnetoresistively, or by means of the Hall effect.
In order to assure a reliable operation of the internal combustion engine, the engine must be prevented from rotating in reverse, or a reverse rotation must be reliably detected. A reverse rotation of the engine can occur, for example, due to an output of incorrect ignition angle data when starting, when the engine stalls, or as a result of inertia forces when the vehicle is in a skid.
In the event of the reverse rotation, the control unit also receives a square-wave signal from the speed sensor, but cannot determine from it whether there is in fact a reverse rotation. If a reverse rotation of the engine goes undetected, then the angular basis in the control unit no longer agrees with the motor position or an incorrect synchronization can occur. This would result in indefinite injections and ignitions. This uncontrolled state of the engine involves a high risk of ignitions when the injection valve is open and therefore a high risk of intake manifold splashing.
In the event of intake manifold splashing, the idle actuator, the throttle valve, or the intake manifold, and possibly also the pressure gauge and the hot film air mass gauge (HFM) can be damaged.
For systems with gasoline direct injection, a reverse rotation detection is particularly important since the charging of fuel into the cylinder is no longer executed as a function of a mechanical coupling, but is executed as a function of the angular basis in the control unit. Consequently, not only the ignition, but also the injection into the combustion chamber can occur at any time. If the injection valve is actuated during starting when the cylinder is already under compression, then it may not be possible to close it again since the counterpressure is too high (high pressure has not yet built up in the rail). As a result, air can get into the high-pressure fuel distribution apparatus and the valve can coke.
In order to obtain sufficient information regarding the current work cycle of the engine, in addition to querying the crankshaft position, the absolute camshaft position must also be detected. The position of the camshaft must also be detected for systems with camshaft adjustment.
In modern systems for controlling the internal combustion engine, the cam shaft position is determined sequentially. Future systems will require continuous camshaft position detection by means of an absolute angle detector.
There are known absolute angle measuring devices for detecting the camshaft position, whose output signal periodically rises or falls a linear fashion depending on the rotation direction of the camshaft, wherein the period corresponds to 360xc2x0 of camshaft rotation or 720xc2x0 of crankshaft rotation. Because the output signal of the camshaft absolute angle measuring device rises or falls in a linear fashion, a matching rotation angle can be associated with, given, or measured for each rotation position of the camshaft.
DE 19722016 has disclosed a device for contactless rotation angle detection, particularly the rotation angle position of the camshaft. In this connection, for example two sensor elements, one of which functions according to the Hall principle and the other of which is a magnetoresistive sensor, are coupled to each other geometrically and are electronically connected via a network, and are subjected to a rotating magnetic field whose rotation correlates to the rotation of the camshaft of the engine. An angle measuring device is thus produced that expresses the rotation angle of a rotating shaft such as the camshaft in the form of a linearly increasing output voltage with a periodic saw tooth when the crankshaft or camshaft rotates in the forward direction, in order for this output to be further processed.
The object of the current invention is to reliably detect, within a small rotation angle, a reverse rotation of the internal combustion engine by means of an absolute angle detector disposed on the camshaft.
This object is attained according to the invention by means of the characterizing part of the main claim.
By querying the absolute angle at particular times, a determination can be advantageously made as to whether the signal is behaving in a monotonously falling manner in order to draw conclusions from this as to whether reverse rotations are occurring. Through the type of reverse rotation detection, it is now possible to suspend the injection output and ignition output. As a result, an operation that is damaging to the engine can be prevented.
Other advantageous embodiments of the invention ensue from the dependent claims.